Many of the games we include in our weekly iPhone and iPad Gems roundups are "me too" releases -- games that we've seen done before on other platforms or by other developers. It's rare that a title actually feels different enough from the pack to merit its own standalone review, but Taplay.com/Chillingo's new iPhone/iPod touch game Monster Mayhem ($2) is an exception: on the surface, it looks like a straight ripoff of PopCap Games' successful tower defense game Plants vs. Zombies, yet despite the obvious inspiration, it turns out to be a very different game that succeeds on its own merits.

Just like Plants vs. Zombies, you’re tasked with stopping the advances of a zombie horde that moves from the right side of the screen towards the left, and as the game progresses, the action is interrupted with trading card-like introductions of new characters. The 20 characters are predictable in concept—faster ones, slower ones, ones who shouldn’t be hurt—but they’re amusingly executed: cartoony wolfmen, Frankensteins, turtlemen, and other monsters that have plenty of personality; six bosses are also included. A vaguely spooky music track plays as you move through the levels, switching as you fight the bosses.

The gameplay is more action-heavy than Plants vs. Zombies. You use an increasing collection of touch-based weapons to stop the monsters directly, starting with a basic knife and gun that slash and fire as you swipe and tap the screen, then buying more weapons—flamethrowers, lightning attacks, and grenades amongst them—with coins that are scattered across the play field as you kill off the monsters. Monster Mayhem’s weapons aren’t anywhere near as creative as PopCap’s plants, but then, there’s something to be said for being able to fire a plain old gun or toss grenades into a crowd of enemies, and Taplay.com makes it all work by restricting your ammo, which acts as a counterbalance to the more direct action. There’s no way to complete the average level using only guns, and buying additional ammunition between rounds costs money; you’ll occasionally luck out and get ammo by dispatching the monsters. With enough cash, you can upgrade your weapons, for instance transforming your knife into a meat cleaver, and increasing the damage it causes.

Where Monster Mayhem begins to get really interesting is in the developer’s use of additional counterbalances that keep the action from being a pure shooting gallery. Spiders descend on your coin bank and can only be killed by your knife, forcing you to switch weapons and hope that your gate doesn’t get knocked down by other monsters while you’re protecting your money. Evil flowers pop up on the field to serve as protectors for the monsters, forcing you to be more careful with bullets, lest you lose ammo and life shooting the flowers. Little elves pop out at the end of some levels to dispense tons of coins and ammo if you knife them, a la Sega’s arcade fighter Golden Axe. Bosses challenge you to do more than just keep firing at the same place on the screen. It all just works, and by stage 2-2—there are 6 multiple-stage graveyards—on the middle level of difficulty, it’s challenging enough that you might well lose.

As was the developer’s obvious intention, the aggressive $2 asking price and intriguing though derivative concept definitely make Monster Mayhem worth checking out if you’re a fan of Plants vs. Zombies—under different circumstances, this game could easily have been either a side story or a full sequel to PopCap’s game. Between its more action-intense gameplay and the high-quality production values, which place it a couple of notches below Plants vs. Zombies, at a lower price, Monster Mayhem is worthy of our strong general recommendation.

Editors' Note: iLounge only reviews products in "final" form, but many companies now change their offerings - sometimes several times - after our reviews have been published.
This iLounge article provides more information on this practice, known as revving.